1. Technical Field of the Invention
The present invention relates in general to time-lapse photography. More specifically, the present invention provides a method for capturing a series of time-lapse photographs with minimal flicker.
2. Description of the Related Art
Time-lapse photography is a technique for capturing a series of photographs over time. In its most dramatic form, a series of images is captured and some slow change occurring in time over the series of images and that may not be otherwise perceptible becomes apparent when time is compressed due to the time-lapse. In its most basic form, time-lapse technology enables a photographer to use his or her camera to capture a series of photographs or film frames at specific intervals of time. Common uses of this technology involve the capturing of videos of the sunset, the motion of stars and clouds in the sky, the blossoming of a bud into a flower, the melting of an ice cube, or the construction of a building, to name a few. Generally, the optimal subject matter of the photos is one exhibiting very slow changes over time; however, in practice any subject may be used. Time-lapse technology and techniques may be used with either a digital camera or in an analog camera, where often either type is controlled and/or adjusted by an external computing device. In other cases, onboard technology may control the time-lapse, such as the “TimeLapse” app by xyster.net, which allows a conventional iPad with camera to essentially become a time-lapse photography generating system. In all cases, after capturing all the desired images, each of the image frames is sequenced with a plurality of others and at a particular frame rate per second so that to the observer the collection of still images appears in sequence to show time moving at a rate much faster than it does in nature.
Because of the way all cameras must handle varying levels of light, time-lapse photography works best when lighting conditions are nearly static throughout the time-lapse. For instance, a flower blooming in a lit room, or in the middle of the bright sunshine over the course of several hours make exemplary subject matter because the only exhibiting great change over the time-lapse is the flower. One well-known problem of the time-lapse technique that can occur when lighting conditions are not static is flickering, or the opposing changes in light luminosity between frames of a time-lapse. Light conditions greatly affect the brightness of the time-lapse photographs, and thus if conditions are changing, such as when clouds occasionally obscure the sun, or the setting or rising of the sun occurs during the time-lapse, then the final motion picture may appear to flicker. This is because what may only be subtle brightness variation between a first image and a second image may actually be processed by the camera in widely varying ways.
A modern camera normally automatically adjusts its image capture settings and parameters to account for the huge variations in the amount of light in the framed image captured by the camera. However, modern cameras also only have a finite number of settings and generally don't allow for the high precision adjustments that would be needed for two very similar images to be processed in a way such that the total brightness of each frame is nearly identical. When a series of time-lapse photographs are taken of an environment with a changing light source by a camera without such precision, flickering may be apparent in the finished animation. That is, the improper or imprecise adjustment of the camera aperture and other settings bring about different brightness levels in different frames of the video. This causes slightly too much or slightly not enough light to enter into the camera, ultimately resulting in flickering of an image sequence in the video.
The above-described problems are most apparent when a time-lapse captures the progression of an environment from either day to night, or night to day. It is known that in an environment of a typical bright day and the environment of a typical a starry night have a light difference of about twenty-one stops, where a stop is a relative measurement of light, typically measured with an f-number (or f-stop), which is the ratio of the lens's focal length to the diameter of the entrance pupil. In order to minimize flickering during time-lapse photography when the light levels are dramatically changing, the camera exposure settings must be changed very gradually over a range greater or equal to twenty-one stops. If done with absolute precision, no flickering would be apparent because the brightness of the image would be identical from frame to frame. However, typical camera exposure settings such as camera aperture and shutter speed cannot be changed gradually or with sufficient precision because the presets are normally spaced at ⅓-stop intervals, even on professional cameras. Thus, changing these settings at even their smallest increments (⅓ stop) causes abrupt brightness changes and the final time-lapse image will exhibit unwanted flicker.
Although the problem occurs whenever light conditions are changing, as may be expected the problem is most apparent during the transition from day to night or night to day, and more particularly during the twilight hours. It just so happens that these times are some of the most popular and dramatic times photographers choose to take a time-lapse animation in the first place. Further, the rapidity of changes during the twilight hours is dependent on the latitude of the viewer. To overcome this problem, the rate of change of the camera exposure settings in the twilight period must be adjusted to account for those changes.
Conventional methods for solving the above-mentioned problems in time-lapse photography involve the post-processing of images wherein by using software the various levels of light from frame to frame are slightly adjusted so that any flickering is reduced. If, for instance, one frame is particularly darker than those around it, the light level of that particular frame may be increased. This method adds a layer of complexity and time to the system that the present invention does away with.
Hence, it can be seen that there is a need for an improved method of generating a series of time-lapse photographs that exhibit minimal flicker, even when light levels are changing. Further, such a method would compensate for the massive difference in amount of light between day and night and allow for the capturing of a time-lapse sunset from full daylight to darkest night or a time-lapse sunrise from darkest night to full daylight. In addition, this improved method would also properly adjust the rate of change of camera exposure settings during the twilight period based on both light levels and the latitude of the system.